Tuilagi was cited for a tip tackle on scrum-half Danny Care two minutes into Leicester’s Aviva Premiership final defeat to Harlequins on Saturday.
The Tigers centre was cleared at a disciplinary hearing on Tuesday after England lawyer Richard QC successfully proved that Care’s knee had hit the ground before his torso.
Although Tuilagi was shown to have controlled Care’s return to the ground on this occasion, Lancaster stressed the need for him to remain vigilant.
“I have had a one-to-one with every member of the touring party. I had a good conversation with Manu on the strengths of his game and the areas we need to make sure he is on top of,” Lancaster said.
“Part of that is tackle technique and discipline. He understands that. He is a young player and still getting experience.”
The independent disciplinary panel backed referee Wayne Barnes, who penalised Tuilagi for the tackle but ruled the tackle was “not dangerous”.
It could have been worse for Tuilagi given the International Rugby Board’s clamp down on dangerous tackles.
“I was relieved. There was a concern,” Lancaster said.
“I am pleased to see the people in charge found it was dealt with on the pitch at the time. I am delighted he is available.”
Lancaster has extended the warning to the whole of his squad ahead of their three-Test series against the Springboks.
“The directive is clear and players are working hard to abide to that,” Lancaster said.
“It is a difficult one, an 11-stone scrum-half comes running at a 17-stone bloke. Danny said the force of the impact took him off his feet. People recognise Manu’s intention was not to hurt anyone.
“We all understand the reason the rule is there. Players just need to be careful if you are picking somebody up.
“When we do video sessions we will highlight areas of ‘red flag’ – things such as the directives around the breakdown, competing for the ball when the referee calls ruck, being onside and tip tackles.”
Once Tuilagi was cleared to play on, Lancaster’s concerns then switched to the foot injury he suffered in the Premiership final.
Tuilagi was cleared to fly with the squad last night but he has not trained since the game.
England will know tomorrow whether he is fit for a return to action next week, ahead of the first Test in Durban.
Phil Dowson, Anthony Allen and Ugo Monye all sat out training yesterday but are expected to be available when the team begin preparations on arrival in South Africa.
England have never before faced the Springboks in a three-Test tour and they have organised two midweek matches, with Lancaster taking a 42-man squad.
“It is a fantastic opportunity to pit ourselves against one of the best rugby-playing nations in the world,” Lancaster said.
“It as a great opportunity for England. We spoke last night about being good ambassadors on and off the field. That is what we want to achieve going into the tour.”
It is England’s first overseas tour since the scandal-hit World Cup campaign and Lancaster has warned he would not tolerate any repeat of the off-field antics which led to England returning from New Zealand with their reputation in tatters.
The England coach took the squad through their code of conduct and hammered his message home by flashing up newspaper headlines on the string of World Cup controversies.
Lancaster cracked down on discipline when he took over the reins from Martin Johnson ahead of the RBS 6 Nations, and he reminded his players they head to South Africa as ambassadors of English rugby.
“I talked about the environment we have created since the World Cup and the reasons why,” Lancaster said.
“I started the talk by reminding the players where we were six months ago and I showed them some of the headlines.
“I said to them, ‘The reason we have got from where we were then to where we are now is because we have focused on why we want to play for England’.
“When you look around the room, there have been quite a few players involved in incidents and all of them were nodding their heads in agreement when I said, ‘We don’t want to have any off-field distractions affecting our on-field performance’.
“That was basically the line. I made it pretty clear – this is the way the bus is going and you all have a decision if you want to be on it.”
England’s World Cup campaign was dogged by controversy, from the drunken night out in Queenstown which led to Mike Tindall being fined £15,000 to Manu Tuilagi jumping from a ferry into Auckland Harbour.
Lancaster has not set any specific curfews on his players and he will not lock them up in the team hotel every night of the five-match, three Test tour.
But he said the squad are in no doubt about what is now acceptable for an England player on tour.